What kind of yogurt are you using?
I know plain fat free is good to use
but I like the yogurt with fruit, and I found one that has no sugar added and low fat, or is better to use the Fat Free fruit flavored yogurt (which has more sugar grams) ?

I hated plain yogurt before I started SB...now, I love plain greek yogurt but flavor it with either cinnamon or nutmeg and sometimes a small handful of berries.

Like Cyndi said, all yogurt is going to have some sugar grams from the natural lactose. Just make sure the yogurt you are using doesn't have added sugar (sucralose or artificial sweeteners are fine), like HFCS or just plain sugar. A LOT of the fruit flavored yogurts have HFCS.

I either add fruit to plain fat free Greek yogurt or I add SF caramel syrup, a little vanilla and Splenda to it and it's fantastic. I have tried the Light & Fit before but wasn't impressed and now I see it has added sugar. It's very difficult to find one that doesn't have some kind of sugar in it.